Skip to main content

​
Overview

Arx is Fabraix’s run-time defence layer for AI agents, informed by what our offensive agent Nyx finds in the wild. The premise is simple: you can’t verify what you haven’t tried to break, and the same research that makes Nyx effective on offence is what makes Arx effective on defence. Arx provides three primary capabilities:
  • Session tracking: register agent runs and correlate every step under a trace_id
  • Event logging: record user inputs, model outputs, tool calls, memory ops, and environment events
  • Action checks: validate actions in the context of the full session before they execute

​
Base URL

All API requests should be made to: 
https://api.fabraix.com/v1

​
Authentication

All requests must include your API key in the x-api-key header: 
curl -H "x-api-key: YOUR_API_KEY" https://api.fabraix.com/v1/endpoint
See the Authentication guide for details.

​
Available Endpoints

POST /register-agent-run

Register a new agent session and receive a trace_id for tracking all subsequent events

POST /event

Log events throughout your agent’s reasoning loop for observability and analysis

POST /check

Validate actions before execution to prevent malicious or unintended behavior

​
Request Format

All POST requests should use JSON format with Content-Type: application/json: 
{
  "field1": "value1",
  "field2": "value2"
}

​
Response Format

All successful responses return JSON with appropriate HTTP status codes: 
{
  "result_field": "value",
  "timestamp": "2024-01-01T12:00:00Z"
}

​
Error Handling

Errors return appropriate HTTP status codes with detailed error messages: 
{
  "error": {
    "message": "Detailed error description",
    "type": "error_type",
    "code": "ERROR_CODE"
  }
}

​
Common Status Codes

StatusDescription
200Success
400Bad Request - Invalid parameters
401Unauthorized - Invalid API key
403Forbidden - Insufficient permissions
404Not Found - Invalid endpoint or resource
429Too Many Requests - Rate limit exceeded
500Internal Server Error

​
Rate Limits

API rate limits depend on your API key type:
Key TypeRequests/MinuteRequests/Hour
Development601,000
Production60010,000
EnterpriseCustomCustom

​
SDK Support

Arx is currently consumed via the REST API directly. Official Arx SDKs are coming soon.
Looking for the Nyx CLI? See the Nyx API reference. The @fabraix/nyx npm package is generally available today.

​
Pagination

For endpoints that return lists (future releases), pagination is handled via query parameters:
  • limit: Number of items to return (max 100)
  • offset: Number of items to skip
  • cursor: Cursor for cursor-based pagination
Example: 
GET /v1/events?limit=20&offset=40

​
Versioning

The API version is included in the URL path. The current version is v1. Breaking changes will result in a new API version. Non-breaking changes may be added to the current version.

​
Webhooks (Coming Soon)

Future releases will support webhooks for real-time notifications:
  • Action blocked events
  • Anomaly detection alerts
  • Session completion notifications

​
Support

Need help with the API?

​
Quick Start Examples

Register a Session

curl -X POST https://api.fabraix.com/v1/register-agent-run \
  -H "x-api-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"agent_id": "123", "timestamp": "2024-01-01T00:00:00Z", "system_prompt": "Helper"}'

Log an Event

curl -X POST https://api.fabraix.com/v1/event \
  -H "x-api-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"trace_id": "abc", "type": "user", "content": "{}", "schema": "{}"}'

Check an Action

curl -X POST https://api.fabraix.com/v1/check \
  -H "x-api-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d '{"trace_id": "abc", "content": "{}", "schema": "{}"}'

Handle Errors

try:
    response = client.check_action(...)
except RateLimitError as e:
    time.sleep(e.retry_after)
    response = client.check_action(...)